1. Water use and water use efficiency in west coast Douglas-fir Paul Jassal, Andy Black, Bob Chen, Zoran Nesic, Praveena Krishnan and Dave Spittlehouse University of British Columbia Vancouver, Canada CFCAS BC FLUX STATION

2. Outline of the talk 4. Effect of stand age 5. Effect of nitrogen fertilization 3. Relationships between physiological and environmental controls of water use and carbon uptake 2. Diurnal, seasonal and interannual variability of water use and water use efficiency 1. BC Flux Station sites Vancouver Campbell River

3. Pole/sapling HDF88 Near mature DF49 Plantation HDF00 BC Flux Station Chronosequence of three coastal Douglas-fir stands 338Height (m)2

4. Water use efficiency Water use or evapotranspiration (E) = mm or kg of water m -2 Water use efficiency = g C m -2 mm -1 or g C kg -1 water as GPP/E or NEP/E GPP = gross primary productivity, i.e., C uptake by photosynthesis (~twice of NPP) NEP = net ecosystem productivity (net C sequestration) = GPP – R In this analysis, EC-measured fluxes have not been corrected for energy balance closure. EBC is approximately 0.81.

5. Physiological and environmental controls Both C uptake by and transpiration from vegetation takes place through leaf stomata with their rates partly determined by canopy conductance, g c. Penman-Monteith equation: Priestley-Taylor equation: Available energy Vapor pressure deficit Canopy conductance Aerodynamic conductance

6. Air temperature Month CC CC

7. Cumulative precipitation Dry months J F M A M J J A S O N D mm

8. Soil water content in the 0-60 cm layer m 3 m -3 Dry months WP FC Month

9. Diurnal variations August 2006 11121314151617 gcgc  mol C m -2 s -1 g m -2 s -1 kPa mm s -1 mmol m -2 s -1

10. Seasonal variations J F M A M J J A S O N D 0 5 10 15 GPP 0 1 2 E 0 10 20 WUE g C m -2 mm -1 or g C kg -1 mm d -1 g C m -2 d -1 2006

11. Seasonal variations in GPP, E and WUE mm mon -1 g C m -2 mon -1 g C m -2 mm -1 Or g C kg -1 Month GPP WUE E

12. Relationship between monthly GPP and E GPP (g C m -2 mon -1 ) GPP = 6.0E –25 r 2 = 0.96

13. Effect of soil moisture on monthly E mm mon -1 Cold Septembers Dry months Wet months 1998 - 2007

14. Effect of soil moisture on monthly GPP g C m -2 mon -1 Cold Septembers 1998 - 2007 Dry months Wet months

15. Relationship between monthly E and net radiation E (mm water mon -1 ) E = 0.1R n + 11 r 2 = 0.94

16. Daytime dry-foliage Priestley-Taylor  Month Correcting for EBC would result in a 25% increase in 

17. Daytime dry-foliage canopy conductance Month mm s -1 5 mm s -1 ~ 220 mmol m -2 s -1

18. Relationship between daytime dry-foliage monthly  and g c  1998 - 2007 + 0.3

19. Modelling daytime dry-foliage monthly g c 1998 - 2007

20. Interannual variations in GPP, E and WUE g C m -2 mon -1 mm mon -1 g C m -2 mm -1 or g C kg -1 Cold & wet DryWarm GPP WUE E Mean: 5.3 g C kg -1 water

21. Effect of stand age and fertilization on annual E Filled triangles are for 2007, the first year after N fertilization 0102030405060 0 100 200 300 400 500 Age (Years) Annual E (mm) Age (years)

22. Effect of stand age and fertilization on annual GPP Filled triangles are for 2007, the first year after N fertilization Age (years)

23. Effect of stand age and fertilization on annual WUE Filled triangles are for 2007, the first year after N fertilization Age (years)

24. Effect of stand age and fertilization on annual NEP NEP = GPP - R C Source C Sink Age (years)

25. Effect of stand age and fertilization on annual WUE based on NEP Filled triangle are for 2007, the first year after N fertilization Age (years)

26. Conclusions Growing season Priestley-Taylor daytime  of about 0.6 was consistent with low canopy conductance (~4.5 mm s -1 ), and suggests stomatal limitation to transpiration. Daytime canopy conductance could be parameterized as a linear function  /D. Water deficit in Jul-Sep decreased E as well as GPP, and explained much of their interannual variability. The high correlation between E and GPP resulted in WUE being relatively conservative with a value of ~5 g C kg -1 water. There was relatively small 1 st year response of GPP & E to N fertilization; NEP in all 3 stands responded to fertilization, due to decreased R, resulting in increased WUE on an NEP basis.

27. Thank you!